1. Field of the Invention
This invention relates to methods for detecting ribonucleic acid (RNA) in bodily fluids such as blood plasma and serum obtained from an animal. Specifically, the invention is directed towards methods for detecting RNA in bodily fluids from a human bearing a premalignant lesion or a malignancy, ranging from localized neoplasia to metastatic disease. The methods of the invention are particularly drawn to detecting mRNA encoding all or a portion of a particular gene, referred to herein as the 5T4 gene. This gene is expressed in many malignant and premalignant tissues, as well as in placental tissue. Since RNA is essential for expressing the 5T4 gene and producing 5T4 protein, detection and monitoring of 5T4 mRNA provides a convenient and reliable method for assessing and monitoring 5T4 gene expression.
2. Background of the Related Art
Pathogenesis and regulation of cancer is dependent upon the translation of RNA to produce proteins involved with a variety of cellular processes, such as cell proliferation, regulation, and death. Particular RNAs involved in these cellular processes include 5T4 RNA; these RNAs are associated with cellular processes characteristic of cancer, such as metastatic potential, invasiveness, and alterations of cell-cell interactions. Furthermore, some RNA and their translated proteins, although not necessarily involved in specific neoplastic pathogenesis or regulation, may serve to delineate recognizable characteristics of particular neoplasms by either being elevated or inappropriately expressed.
The 5T4 protein encoded by said RNA is a transmembrane glycoprotein normally present in trophoblast tissue whose gene structure has recently been characterized (Hole & Stem, 1988, Br. J. Cancer 57: 239-246; Hole & Stern, 1990, Int. J. Cancer 45: 179-184; Myers, 1994, J. Biol. Chem. 269: 9319-9324; King et al., 1999, Biochimica et Biophysica Acta 1445: 257-270). The protein is expressed at low levels in cells of only a few other normal epithelia. Significantly, 5T4 expression is upregulated in cells comprising many cancers and premalignant tissues, including but not limited to cancers of breast, ovary, lung, cervix, colorectum, stomach, pancreas, bladder, endometrium, brain, kidney, and esophagus (Jones et al., 1990, Br. J. Cancer 61: 96-100; Southall et al., 1990, Br. J. Cancer 61: 89-95; Starzynska et al., 1992, Br. J. Cancer 66: 867-869; Starzynska et al., 1994, Br. J. Cancer 69: 899-902). Because of this, 5T4 mRNA is considered herein to be a tumor-associated RNA. Overexpression of 5T4 is particularly associated with cancers of high metastatic potential and poorer prognosis (Mulder et al., 1997, Clin. Cancer Res. 3: 1923-1930; Starzynska et al., 1994, ibid.). Detection of 5T4 thereby permits detection and monitoring of a wide spectrum of cancers and premalignancies, and may have prognostic significance. 5T4 further provides a target for cancer therapies, particularly monoclonal antibody-based therapies and vaccine therapies.
RNAs associated with cancer and premalignancy have been characterized as tumor-derived, and are termed “tumor-associated RNA” herein. Co-owned and co-pending U.S. patent application Ser. No. 09/649,371, incorporated by reference herein in its entirety, provides methods for detecting tumor-associated or tumor-derived 5T4 RNA in bodily fluids such as blood plasma and serum, wherein said RNA detection is used for the detection, monitoring, or evaluation of cancer or premalignant conditions.
Another biological phenomenon in which RNA and translated proteins therefrom are fundamentally involved is the cascade of events that occur during pregnancy. Such RNAs assist in the rapid growth of specific tissues during pregnancy, being principally those of the embryo and those of the placenta, wherein placental tissue includes fetal trophoblast tissue. 5T4 is normally present in fetal trophoblast tissue, so that detection of 5T4 RNA in bodily fluids such as blood, including blood plasma and serum, from pregnant or recently pregnant women, enables the monitoring of placental conditions and states in these women, both normal and pathologic. Examples where such monitoring would be advantageous include but are not limited to monitoring of placental growth during pregnancy, evaluation of deleterious conditions associated with pregnancy such as preeclampsia and eclampsia, evaluation for retained placenta following normal delivery or following spontaneous or incomplete abortions or medical terminations of pregnancy, and monitoring of gestational trophoblastic diseases. In contradistinction with the invention disclosed herein, which enables detection of RNA specific for the trophoblastic (placental) compartment of conception rather than the entire fetal compartment (including the embryonic compartment), the presence of fetal RNA in blood plasma has recently been described (Poon et al., 2001, Clin. Chem. 47: 363, Abst. No. 11).
5T4 RNA being recognized herein as a tumor-associated RNA, there is a heretofore unappreciated need in the art to identify premalignant or malignant states characterized by 5T4 in a human by detecting 5T4 RNA in bodily fluids such as blood plasma or serum. Similarly, since 5T4 is a normal trophoblastic protein, a blood test for 5T4 mRNA in pregnant or recently pregnant women without cancer would be useful for diagnosing complications of pregnancy.